1. Field of the Invention
The present invention is generally in the field of semiconductors. More particularly, the present invention is in the field of one-time programmable semiconductor devices.
2. Background Art
One-time programmable (OTP) devices are used throughout the semiconductor industry to allow for post-fabrication design changes in integrated circuits (ICs). For example, after post-fabrication functionality testing but before sale to a customer, a semiconductor device manufacturer can program a network of OTP devices embedded in a particular semiconductor die to provide a permanent serial number encoding for that particular die. Under other circumstances, a single OTP device can be programmed to permanently enable or disable a portion of an integrated circuit at any time after fabrication, including after sale to a customer. Although this functionality is in great demand, conventional OTP elements (the programmable constituent of an OTP device) can be larger than desired or can require multiple additional fabrication steps beyond those required for conventional transistor fabrication, for example, making conventional OTP devices expensive to manufacture and embed.
One such conventional embedded OTP device can be fabricated using the so-called split-channel approach, where an atypical metal-oxide-semiconductor field-effect transistor (MOSFET) fabrication process is used to form a gate structure comprising a single channel interface with two different gate dielectric thicknesses. The thin portion of gate dielectric (the OTP element) can be made to destructively break down and form a conductive path from gate to channel, thereby switching the conventional OTP device into a “programmed” state. This approach, however, has a relatively high tendency to result in devices with programmed states where the remaining thick gate structure exhibits a high leakage current due to collateral damage during programming. In addition, this approach tends to render devices with relatively poorly differentiated programmed and un-programmed states (as seen by a sensing circuit), which, in combination with the high leakage current statistics, require a relatively high voltage sensing circuit to reliably read out programmed and un-programmed states. Mitigation of these shortcomings can require additional die space for high-voltage sensing circuitry and/or for redundancy techniques, for example, which can involve undesirable increases in manufacturing cost.
Thus, there is a need to overcome the drawbacks and deficiencies in the art by providing a reliable OTP device that is both robust against damage during programming and capable of being fabricated using existing MOSFET fabrication process steps.